Power management implementation in an optical link

ABSTRACT

An optical link power management scheme takes the best advantage of a dynamic connection environment, where ports may be connected and disconnected at any time, and where data flows may start and stop as needed by the applications using the high speed data links. Power consumption is optimized, eye safety standards are met, and robust connection detection is preserved.

FIELD OF THE INVENTION

Embodiments of the present invention are directed to optical links and,more particularly, to optical links which may save power when theoptical link is unplugged and maintain eye safety standards.

BACKGROUND INFORMATION

Most optical links to date are used in the telecom and datacomindustries, where optical modules tend to be connected duringinstallation, and stay connected for the life of the equipment. Theseconnections stay active as long as the link is connected, neverswitching off once started.

Optical links to be used in a consumer application may have differentrequirements, as the links are used dynamically, with devices beingplugged and unplugged from the systems. In this case, it is desirable tosave power when a port is not being used, insure that the port meets eyesafety standards when the fiber is not connected, and that the port isable to robustly and reliably detect connections as they occur.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and a better understanding of the present invention maybecome apparent from the following detailed description of arrangementsand example embodiments and the claims when read in connection with theaccompanying drawings, all forming a part of the disclosure of thisinvention. While the foregoing and following written and illustrateddisclosure focuses on disclosing arrangements and example embodiments ofthe invention, it should be clearly understood that the same is by wayof illustration and example only and the invention is not limitedthereto.

FIG. 1 is a plan view of a universal serial bus (USB) device withoptical capabilities, such as a light-peak (LPK) device;

FIG. 2 a dual simplex optical link according to one embodiment of thepresent invention; and

FIG. 3 timing diagram illustrating low speed optical pulses (LSOPs) forpower management of an optical link according to one embodiment.

DETAILED DESCRIPTION

Meeting the simultaneous requirements of low power during idle times,eye safety, and robust connection detection requires the implementationof a power management scheme for the optical link.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, theappearances of the phrases “in one embodiment” or “in an embodiment” invarious places throughout this specification are not necessarily allreferring to the same embodiment. Furthermore, the particular features,structures, or characteristics may be combined in any suitable manner inone or more embodiments.

Referring now to FIG. 1 there is shown an example of a universal serialbus (USB) device with additional optical capabilities for achieving evengreater bandwidths. The USB device 100 has been referred to as theso-called Light Peak (LPK) optical USB. As shown, a cable 102 may joinwith a plastic housing 104. A plug head 106 may include openings 108 inthe head 106 used to lock the connector in place when plugged into acorresponding female connector. Optical ports 110 and 112 may be housedin the head 106 to provide optical capabilities. Optical port 110 mayfor example be to connect to an optical transmitter (Tx) module andoptical port 112 may connect to an optical receiver (Rx) module.

Referring to FIG. 2, there is shown a dual simplex optical linkaccording to one embodiment of the present invention. In the Light Peakimplementation, the components involved comprise a Light Peak SwitchPort (LPK-SP) 200 and a Light Peak Optical Module (LPK-OM) 202. TheLPK-OM 202 may comprise an optical transmit (Tx) module 204 and anoptical receiver (Rx) module 206. Control and data signals 208 and 210between the LPK-SP 200 and the LPK-OM 202 select the various powerstates of the module 202 and directly control the on/off conditions ofthe laser transmitter 204.

The optical receiver 206 may also be placed in the various power states,and then uses the received optical signals to indicate link states tothe receiving portion of the LPK-SP 200. A complete optical link maycomprise a LPK-SP 200 and LPK-OM 202 on one side, an optical fiberconnection 212, and another LPK-OM 302 and LPK-SP 300 on the other side.Each link is dual-simplex, with each side having a transmit channelconnected to the opposite side receive channel. A separate fiber may beused for each direction, with both fibers 212 contained in the sameoptical cable.

Future implementations may combine the LPK-SP 200 and LPK-OM 202 into amore integrated unit, where the control and data Signals 208 becomeinternal to the design. However, the power management functionality andstates being used to control the optics would still exist.

Another option may be the integration of the LPK-OM 202 into amechanical connector eliminating the fiber jumper from the LPK-OM 202 tothe LPK Port Connection 215, and building the system side of the portconnection directly into the mechanical connector. This scheme alsowould not alter the power management functionality between the LPK-SP200 and the LPK-OM 202; it only changes the physical connection of theLPK-OM optical interface.

Future implementations may also include additional high speed signals,implemented as additional fibers and/or additional wavelengths of lightsharing a single fiber or multiple fibers. Power managementfunctionality would also be required for these implementations. In fact,the power management may become more critical in meeting eye safetycriteria, as the additional optical signals may increase the opticalpower being carried by a connection.

When an optical port has no connection, it is desirable to save as muchpower as possible, and it is desired to meet eye safety standards. Thisis achieved by placing the optical module into a very low power Standbystate, where the transmit laser 204 is disabled most of the time. Thetransmit stage 204 consumes almost no power while the laser is disabled.At the same time, the receive stage 206 has minimal functionality, whereit only needs to detect the presence of low speed optical pulses (LSOP)and signal these pulses to the LPK-SP 200.

In order to actually detect a connection, the transmit stage 204 ispulsed on periodically, with a very low duty cycle, low speed pulse. Thepulse represents below a 0.25% duty in one embodiment. This saves asignificant amount of power for transmit stage 204 and easily meets theeye safety standards for an open port. When a physical connection ismade, by connecting optical fiber between the two sides of the link, thelink partner receiver 302 would detect the low speed optical pulse(LSOP), and signal the reception to the LPK-SP 300. At this point, theLPK-SP 200 can begin the detection process.

For robust connection detection, including the avoidance of falseconnection detection, the LPK-SP 200 may use a number of LSOPs to bereceived before deciding that a connection exists. For example, threepulses in a row, with no missing pulses, may be used to indicate that afiber is connected. Once the pulses have been detected, the LPK-SP 200commands the LPK-OM 202 to transition to a higher power Idle state,where more functionality is enabled and where higher speed responses arepossible. The connection uses a modified LSOP, with a somewhat higherduty cycle of about 1% to signal to the link partner that the Idle statehas been activated. The LPK-SP 200 and LPK-OM 202 continue thissignaling until both sides of the link are in the same state. That is,the LPK-SP 200 is both sending and receiving the modified LSOP.

Once both sides of the link are signaling the modified LSOP, the link istransitioned to the Active state, using a different LSOP signal calledRESUME. While in the Active state, the optical link is fully functional,sending high speed data from each transmit stage to the link partnerreceive stage. This involves higher power consumption, as all high speeddata circuits are operational, and the optical signal is being modulatedwith the high speed data. Since the optical fibers are now connected inthe link, the eye safety standards allow a higher power optical signalto be transmitted, as the signal will not be exposed to an open portwhile the fiber is connected.

The above described connection signaling scheme is illustrated in FIG.3. When the optical link is not connected 400 the optical link is in astandby state and disabled most of the time as shown pulsing at a dutycycle below 0.25% using very little power and easily meeting eye safetystandards. Once connected the link goes into a connected standby state402 and the transmitter pulses a number of pulses, for example three lowspeed optical pulses, in a row signaling the receiver on the other sidethat a connection has been made. The optical link then transitions to ahigher power Connected Idle state 404, for example a 1% duty cyclepulses, where more functionality is enabled and where higher speedresponses are possible. This enables detection of a shorter durationRESUME pulse 406 to transition to an Active state 408 wherein theoptical link is fully functional, sending high speed data from eachtransmit stage to the link partner receive stage.

Once in the Active state 408, the link can transition back and forthbetween Active and Idle without the fiber being disconnected. Thisrepresents another opportunity to save power in cases where there is apause in the data flow. Since the fibers stay connected, it is possibleto quickly transition back and forth between the Active and Idle states,as needed. During extended Idle states, the transmit stages send anotherLSOP signal, call CONNECT, to indicate that the fibers are stillconnected and that the link is still enabled. Note that the transitionbetween Active and Idle can be independent in each fiber direction, soone link partner could be sending high speed data to the correspondingreceive stage, while that transmit stage is signaling only the CONNECTpulses in the opposite direction.

If the fibers are disconnected from an enabled link, either on purpose,or due to a fault, the receive stage will no longer be receiving anyoptical signal, and the LPK-OM 202 will signal this case to the LPK-SP200. If the receive stage was in the Idle state, receiving only theCONNECT LSOP signals, these signals will also no longer be detected.This would be the indication that the link has been disconnected. Atthis point, the LPK-SP 200 will disable the transmit stage, to againcomply with the eye safety standards, then the LPK-OM 204 back to theStandby state, where it will wait for another connection.

In the case of multiple fiber or multiple wavelength connections, theconnection detection can be performed on one fiber or wavelength at atime in order to keep the eye safety classification as low as possible.Other signals would stay disabled until a connection is establishedthrough the primary control signals. The disconnect from an enabledlink, either on purpose, or due to a fault, is performed on each fiberand wavelength independently and the link is fully disabled to complywith the eye safety standards. The multi channel connection is thenplaced in the Standby state, where it waits for another connection bysending LSOP on one fiber or wavelength at a time.

The LPK-OM 204 should maintain the eye safety limits even when faultsoccur that would cause the optical signals to exceed these limits.Circuitry exists to shut down the laser in any fault situation; open,hardware short, or software issue, that would cause a violation to theeye safety limits.

This power management scheme takes the best advantage of a dynamicconnection environment, where ports may be connected and disconnected atany time, and where data flows may start and stop as needed by theapplications using the high speed data links. Power consumption isoptimized, eye safety standards are met, and robust connection detectionis preserved.

As a side benefit, running the transmit lasers in a higher power modeafter the fibers are connected allows a larger range of laser transmitpower to be used than has been the case in traditional telecom ordatacom connections. This enables higher production yields for thelasers, larger link margins with similar eye safety classifications, andlower costs for the optical modules. This benefit would not be possiblewithout the power management scheme to keep laser power very low whilethe fibers are disconnected.

The above description of illustrated embodiments of the invention,including what is described in the Abstract, is not intended to beexhaustive or to limit the invention to the precise forms disclosed.While specific embodiments of, and examples for, the invention aredescribed herein for illustrative purposes, various equivalentmodifications are possible within the scope of the invention, as thoseskilled in the relevant art will recognize.

These modifications can be made to the invention in light of the abovedetailed description. The terms used in the following claims should notbe construed to limit the invention to the specific embodimentsdisclosed in the specification and the claims. Rather, the scope of theinvention is to be determined entirely by the following claims, whichare to be construed in accordance with established doctrines of claiminterpretation.

What is claimed is:
 1. A method, comprising: sending from an opticalmodule periodic low speed optical pulses (LSOPs) when the optical moduleis disconnected for a Standby State; connecting the optical module to aconnection port; sending a number of consecutive LSOPs for a ConnectedStandby State at a first duty cycle rate; sending LSOPs at a secondhigher duty cycle rate for a Connected Idle State; sending a shorterduration LSOP to initiate a Resume State; and entering an active stateto transmit high speed data.
 2. The method as recited in claim 1 whereinthe optical module comprises a light peak optical module.
 3. The methodas recited in claim 1 wherein the first duty cycle rate is a 0.25% orless duty cycle rate.
 4. The method as recited in claim 1 wherein thenumber of LSOPs for a Connected Standby State comprises three.
 5. Themethod as recited in claim 1 wherein the second duty cycle rate for aConnected Idle State comprises approximately a 1% duty cycle.
 6. Themethod as recited in claim 1 wherein the optical link can transitionbetween states.
 7. The method as recited in claim 1 wherein the LSOPs inthe Standby State meets eye safety standards.